Astronomy Picture of the Day 01-30-04

Explanation: Why do x-ray rings appear to emanate from a gamma-ray burst? The surprising answer has little to do with the explosion itself but rather with light reflected off sheets of dust-laden gas in our own Milky Way Galaxy. GRB 031203 was a tremendous explosion -- a gamma-ray burst that occurred far across the universe with radiation just arriving in our Solar System last December 3. Since GRBs can also emit copious amounts of x-rays, a bright flash of x-rays likely arrived simultaneously with the gamma-radiation. In this case, the x-rays also bounced off two slabs of cosmic dust nearly 3500 light-years distant and created the unusual reflections. The longer path from the GRB, to the dust slab, to the XMM-Newton telescope caused the x-ray light echoes to arrive well after the GRB.

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Opportunity could drive off lander base Saturday night
BY JUSTIN RAY
SPACEFLIGHT NOW
Posted: January 29, 2004

Launched to Mars folded and crouched in its landing cocoon, NASA's Opportunity rover has nearly completed the complex blossoming into a road-ready vehicle and could take its first drive onto the Red Planet's surface Saturday night.

An artist's concept shows a Mars Exploration Rover on the move. Credit: NASA/JPL

The post-landing transformation began soon after touchdown last Sunday morning as the lander base opened and the rover extended its solar panels and camera mast. The lollipop-shaped main communications antenna began service earlier this week, and the past few days have been dedicated to deploying the wheels and suspension system.

Opportunity was jacked up Wednesday, allowing the front two wheels to unfold and the rocker-bogie suspension system to lock into place. The rear wheels extended Thursday to give the vehicle the desired wheelbase length. The center wheels were scheduled to be lowered into position early Friday.

Also Friday morning, the multi-jointed arm holding the science instruments for close-up examination of the Martian soil and rocks was to be unlatched from its launch location and stowed in the "drive" position.

Controllers say if all continues to go as smoothly as the past week, Opportunity will make a 10-foot drive off the lander base and onto the small crater floor Saturday night/Sunday morning to begin its exploration mission of Meridiani Planum.

To help the rover's journey off the lander, which engineers consider the riskiest drive that the craft will take on Mars, Mission Control on Thursday commanded a further retraction of the airbags on the back side of the lander and then forced the rear petal downward. This was designed to prop up the rear of the lander, thereby tilting the base forward for Opportunity to drive off.

"What this did is drive our front edge lower," said mission manager Matt Wallace. "The tips of the egress aid (a reinforced fabric ramp) are now in the soil. That makes egress look perfect. It's going to be an easy ride."

The Spirit rover's drive off its lander earlier this month was complicated by airbags hampering the preferred path. Unable to simply roll straight onto the surface, Spirit had to make a 115-degree turn on the base to reach an alternate driveway. Opportunity has no such obstacle.

On the science agenda Thursday, Opportunity used the Mini-Thermal Emission Spectrometer to survey the mineral composition of the immediate surroundings, including the rock outcrop. Opportunity did not return the data from those observations before going to sleep for the Martian night, but may Friday, officials reported.

The Spirit rover located half-a-world away was receiving commands from Earth Thursday to resume its scientific work at Gusev Crater. Panoramic camera images of nearby rocks were to be snapped.

Also, controllers were hoping to receive a playback of Mossbauer Spectrometer and Alpha Particle X-ray Spectrometer data obtained during last week's study of a pyramid-shaped rock, nicknamed Adirondack. The information was collected but not yet relayed to Earth when Spirit's computer troubles began.

The Jet Propulsion Laboratory reported several attempts to get a full trace of the rover's problem have only partially succeeded. The engineers might choose to reformat the rover's flash memory in the next few days.

"We know we still have some engineering work to do, but we think we understand the problem well enough to do science in parallel with that work," mission manager Jennifer Trosper said.

There was no Mars rover status news conference Thursday. The next briefing is scheduled for Friday at 12 noon EST (1700 GMT).

Fitful young star sputters to maturity in Rosette Nebula
NATIONAL OPTICAL ASTRONOMY OBSERVATORY NEWS RELEASE
Posted: January 29, 2004

A duo of Chinese and American astronomers have discovered a young star in the fierce environs of the Rosette Nebula that is ejecting a complex jet of material riddled with knots and bow shocks.

A newly reprocessed image of the Rosette Nebula (NGC 2237). In this image, a box has been drawn around the zoomed in area containing the jet Rosette HH1, and represented in the images below. Credit: T. Rector/University of Alaska Anchorage, WIYN and NOAO/AURA/NSF
Download a larger version of image here.

Stripped of its normally opaque surroundings by the intense ultraviolet radiation produced by nearby massive stars, this young stellar object is likely one of the last of its generation in this region of space. Its tenuous state of existence exposes the limitations that young stars--and perhaps even sub-stellar objects such as brown dwarfs and large planets--face in attempting to form in such a violent environment.

"Most young stars are embedded in very dense molecular clouds, which makes our view of the early stages of star formation normally impossible with optical telescopes," says Travis Rector of the University of Alaska Anchorage, co-author of a paper on the young stellar object (YSO) in the December 2003 issue of Astrophysical Journal Letters. "This is one of only a few cases where a protostar is visible, making it a valuable discovery that will be studied in detail."

Optical images of the jet taken at the WIYN 0.9-meter telescope at the National Science Foundation's Kitt Peak National Observatory in Arizona show a highly-collimated jet, now known as Rosette HH1, stretching for more than 8,000 astronomical units (1 AU = 150 million kilometers). It contains a prominent knot and hints of others, which can be interpreted as "bullets" of material being ejected from the rapidly rotating YSO at hypersonic velocities on the order of 2,500 kilometers per second. Bow shocks on the other side of the YSO suggest the existence of a degenerated counterjet extending in the opposite direction.

In this zoomed image of the jet, an arrow has been drawn to indiate the Young Stellar Object, Rosette HH1. Credit: T. Rector/University of Alaska Anchorage, WIYN and NOAO/AURA/NSF

These interpretations of the jet were bolstered by optical spectroscopy of the jet system taken by co-author Jin Zeng Li of the Chinese Academy of Sciences in Beijing using the 2.16-meter telescope of the National Astronomical Observatories of China.

"If it is indeed a counterjet, it may be the only existing observational evidence of how bipolar jets evolve into monopoles, or at least highly asymmetric jets," according to Jin Zeng Li. "This suggests that this infant star has been starved of material as its accretion disk is evaporated, leaving a very low-mass star. In some cases, this process might result in an isolated brown dwarf or planetary mass object, offering a potential evolutionary solution for such lone objects that have been spotted in the Orion Nebula and other nearby hotspots in the Milky Way."

Located an estimated 1,500 light-years from Earth in the constellation Monoceros, the Rosette Nebula is a spectacular region of ionized hydrogen excavated by the strong stellar winds from hot O- and B-type stars in the center of the young open cluster NGC 2244. It is a region of on-going star formation with an age of about three million years.

Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, Tucson, AZ, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation.

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